The study - published in the Lancet Public Health journal - goes some way to ending the decades-old debate about whether cutting carbs or fat is the best way to improve health.
The healthiest approach, it suggests, is to eat a balanced diet with nutrients in moderation.
And it raises concerns that the increasingly popular all-or-nothing 'exclusion' diets can do severe damage to people's health.
The findings also support the advice of Public Health England - which suggests starchy carbohydrates should form the main components of a healthy diet.
The US scientists also looked at the combined results of previous studies including 432,000 people from more than 20 countries, which confirmed their findings.
They found that the biggest risk of cutting carbohydrates was if people replaced it with meat and cheese.
If they instead started eating more plant-based food - such as vegetables, lentils, beans and nuts - the risk was lower.
Researcher Dr Sara Seidelmann, of Brigham and Women's Hospital in Boston, said: 'We need to look really carefully at what are the healthy compounds in diets that provide protection.
'Low-carb diets that replace carbohydrates with protein or fat are gaining widespread popularity as a health and weight loss strategy.
'However, our data suggests that animal-based low carbohydrate diets, which are prevalent in North America and Europe, might be associated with shorter overall life span and should be discouraged.' The authors recruited 15,528 adults aged 45 to 64, and then tracked them for 25 years.
Of the original group, 6,283 people died over the study period.
But those who had low carb consumption were 20 per cent more likely to die than those with a moderate consumption.
The researchers extrapolated these results to estimate that someone who was aged 50 with a moderate carbohydrate intake could expect to live another 33 years - taking them to age 83.
Those with a low carbohydrate intake could expect to live to 79 - four years fewer.
And those with a high carb intake could expect to live to 82, one year less than the moderate group.
Co-author Professor Walter Willett of Harvard School of Public Health, said: 'These findings bring together several strands that have been controversial.
'Too much and too little carbohydrate can be harmful but what counts most is the type of fat, protein, and carbohydrate.' And researcher Professor Scott Solomon of Harvard Medical School said: 'This work provides the most comprehensive study of carbohydrate intake that has been done to date, and helps us better understand the relationship between the specific components of diet and long term health.
'These data suggest that shifting towards a more plant-based consumption is likely to help attenuate major morbid disease.'
Dr Andrew Mente from McMaster University in Canada, writing in a linked comment, said eating anything in moderation was advisable - and a 'U-shaped' mortality curve could probably be seen for any nutrient.
He led a study published in the Lancet last year, which found that extremely low-fat diets could also do more harm than good.
Dr Mente says there a 'sweet spot' of consumption levels for all nutrients - and eating too much or too little will be damaging.
'Essential nutrients should be consumed above a minimal level to avoid deficiency and below a maximal level to avoid toxicity,' he wrote.
'On the basis of these principles, moderate intake of carbohydrate is likely to be more appropriate for the general population than are very low or very high intakes.' British scientists also backed the findings.
Dr Ian Johnson of the Quadram Institute Bioscience, a food research centre in Norwich, said: 'The risk of death was convincingly shown to be lowest in those participants who obtained about half their calories from carbohydrates.
'This figure is close to the average carbohydrate consumption by the UK population observed in dietary surveys.
'These findings emphasise that there is nothing to be gained from long-term adherence to low-carbohydrate diets rich in fats and proteins from foods of animal origin.'
Professor Tom Sanders of King's College London added: 'The bottom line is that a balanced diet providing about half of the food energy from carbohydrates is best for health.'
